Process for increasing the degree of oil extraction

ABSTRACT

A process for increasing the degree of extraction of oil or other volatile liquids in oil reservoirs on land or at sea, by making the formations in said reservoir vibrate as close to the natural frequency of said formations as possible, so that the binding forces between formations and oil are degraded and oil is, thus, more easily recovered from the formations. Furthermore, the pressure in said reservoir is maintained by evaporating some oil and water in the reservoir, due to the fact that heating is achieved both as a consequence of said vibrations, and by the aid of electrical high frequeny pulses causing the reservoir to perform like an electrode furnace.

The present invention relates to a process for increasing the degree ofextraction for oil or other volatile liquids in oil reservoirs on landor at sea by the aid of vibrations and heat by the aid of electricalhigh-frequency pulses.

In connection with recovery of oil from any oil field only part of theoil present can be recovered. The degree of recovery can vary fromapproximately 17% and up to approximately 50%. The degree of recoveryfrom the EKOFISK field is, e.g. estimated at approximately 20%.

The cause of the fact that it is not possible to recover all oil from afield, or at least a larger portion of such oil, is involved with themanner in which oil is bound in the formations. Oil in the pores of theformations is bound to said formations by capillary forces, surfacetensions, polar forces, and adhesive forces. At the beginning of oilproduction said binding energy will be overcome by the natural pressureprevailing in said oil reservoirs, but as this pressure graduallydecreases said forces will exceed the expelling pressure, resulting in adecreased oil production even though most of the oil is left in theformations.

Considerable effort was made over the years and is still made toincrease the degree of recovery, and the best known approach is toinject water into the reservoirs. Additionally, a series of chemicalswas developed, all of them more or less intended for breaking up theadhesion forces between oil and formations. Besides being very expensivethe known methods only contribute very little to increase the degree ofrecovery. E.g., the above mentioned degree of recovery is calculatedafter injection of water into the reservoir. Without such injection thedegree of recovery is calculated to be approximately 17%.

Apart from the fact that a relatively small increase of the degree ofrecovery is achieved, water injection requires extensive control ofinjection wells. This is associated with the so called "finger problem"arising when water penetrates. The water front moving in the oil fieldwill not appear as a sharp front, but rather like a front with extended"fingers", due to the fact that water will always seek to find the lineof least resistance in the formation. This may be compared withobservations made when water is spurted onto a mound of gravel. You willsoon observe that the water digs depressions where water can pass. Thehazard of water injection is that such a "finger" reaches the productionwell. In that case only water will be produced from the injection. Inorder to overcome these problems much work is done to develop verysofisticated computer models of these so called front movements in orderto permit control of both volume and pressure of water to preventbreak-through to production wells.

A natural manner of increasing the degree of recovery would be toovercome the above mentioned binding forces with an increase of thepressure within the formations, and not with a pressure front of wateror another expelling medium.

It is an object of the present invention to disclose a process forachieving this aim on the basis of comprehension of the binding forcesacting in a typical oil reservoir.

The process should state the necessary elements for achieving theintended effect and the technique used to this end.

From physics it is known that the frictional force between bodies willdecrease dramatically if one body is rapidly moved normally to thedirection of movement of the other body. This fact is, inter alia, usedwhen certain instruments are supported, i.e. a marker of an instrumentfor detecting some physical change is mounted on a slide bearing on around rod. When said rod is rotated the frictional force between saidbearing and rod will be approximately 0. The same effect may, indeed, beobserved when we hit the cover of, e.g. an oil drum, if there is alittle sand and water on said cover. Both sand and water will "float" onthe cover like small drops, and there is only a minimum force needed toblow the drops away.

The first part of the process has the object of establishing vibrationsof an oil reservoir to achieve the same effect of the oil trapped in theformations.

So long as there is a natural pressure in the reservoir this will beenough to squeeze out considerably more oil than from a reservoir "inpiece and quiet". Even though a considerably lower pressure is necessaryto recover more oil from the field, sooner or later, there will be alimit of how much oil you can recover from the field. When the naturalpressure disappears there are two conceivable manners of recoveringoil--pumping by suction, which is e.g. used in so called "nodding pumps"and/or creating a new pressure inside the reservoir.

Since there is still a considerable volume of oil remaining in thereservoir it represents a liquid which could, by evaporation, create thenecessary internal pressure to increase the degree of recovery.

It is suggested that such evaporation of the oil may be achieved byheating the field by the aid of electrical high-frequency currentspassing between the different wells that are commonly drilled from aproduction rig. Since there is always a little brine in an oil fieldand/or such brine can be supplied by injection and to the extent waterbreak-through is achieved between the separate wells anelectroconductive medium will be obtained which will act as an electrodefurnace when electric energy is supplied. The resulting energy willcause evaporation of oil/water and will, thus, increase the pressure sothat more oil can be recovered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of several wells drilled according to theinvention.

FIG. 2 is an enlarged view of the lower portion of a well according tothe invention.

FIG. 3 is a sectional view of three wells showing vibrational andelectrical waves.

FIG. 4 is a sectional view of two wells and the "finger problems" thatarise with water flooding.

FIG. 5 is a section of a well using two vibrators.

DETAILED DESCRIPTION OF THE INVENTION

The process is now explained in more detail with reference to thedrawing:

FIG. 1 shows a sectional view of an oil reservoir where several wells ahave been drilled. Into the lower portion of the well, where oilrecovery takes place, mercury b or another heavy electroconductiveliquid was poured. The function of said liquid is both to conductvibrations to the surrounding formations c, to conduct electric currentfrom one well to another, and also to "flash" out oil/water, andpossibly mud produced below liquid level d.

A high-frequency vibrator is via a cable e provided in liquid b and issupplied with energy from the surface by a high-frequency convertorwhich is, in turn supplied with energy from a generator h. This energyis conducted down to said vibrator by conductors in the center of cablee. Said conductors are surrounded by an insulator j onto which aconductor k is wound which is connected in an electroconductive mannerto the surface 1 of said vibrator.

Conductor k receives energy from a high-frequency convertor n which, inturn, receives its energy from a generator o. Said generator andfrequency convertor can supply both single phase and polyphase current.In case of single phase current each phase goes to a well and in case ofthree-phase current 3 wells are connected to phases R, S, T.

Electric current may also be conducted down to the well through pipes smade from steel or another electroconductive material conventionallyused for well liners. In this case only conductors for supplying energyto the vibrator itself by the aid of conductor i are required. Liquid b,also, does not have to be electroconductive in this case.

FIG. 2 shows an enlarged view of the lower portion of two wells p withan auxiliary well q, and an illustration of a break-through of water r.

When said vibrator receives energy it will oscillate the mercury b withvibrations adapted to the natural frequency of the formations, saidnatural frequency being defined as the frequency of the undamped freevibration, that will cause resonant vibrations in said formations whichvibrations will propagate outwards and will, literally shake off the oilfrom the formations. The energy from vibrations will also supply theformations with heat as frictional heat between separate particles ofthe formation and between the formations and the oil flowing out, and itwill contribute to maintaining the pressure by evaporating some oil andwater.

When energy is supplied to the surface of vibrators it will be conductedoutwards to the surrounding formations through the mercury and it willpropagate further outwards in the field to next pair of poles in thenext well. The same will happen if the current is conducted down intothe well through the liners. Conductivity will increase if there is abreak-through of water and this will, in fact, contribute to increasethe development of heat in the formations. If the formations are suchthat it is impossible to achieve electrical contact between twoproduction wells p so called auxiliary wells may be drilled in which thesame kind of vibrators/electric conductors are provided.

FIG. 3 shows a sectional view of three wells indicating how vibrations tand the electric field u propagate between wells.

FIG. 4 is a sectional view of two wells indicating the "finger problem"that may arise when water is injected.

FIG. 5 shows a section of a well illustrating an arrangement comprisingtwo vibrators and indicating the waves of vibration and the field linesfrom the electric voltage going down into the mercury.

I claim:
 1. A process for increasing the degree of extraction of oil orother volatile liquids in oil reservoirs on land or at sea, by makingthe formations in said reservoirs vibrate as close to the naturalfrequency of said formations as possible, so that the binding forcesbetween the formations and oil are degraded, and by electric stimulationby means of electrodes placed in at least two adjacent well bores, theimprovement comprising filling a well bore with a metallic liquid in aheight zone corresponding to the height of the formation, vibrating saidmetallic liquid by means of an inserted vibrator, and at the same timeperforming an electric stimulation by applying an alternating electriccurrent to said electrodes.
 2. A process according to claim 1, in whichthe metallic liquid is mercury.
 3. A process according to claim 1, inwhich more than one vibrator is used in the said well bore.
 4. A processaccording to claim 1, in which electric current is supplied to themetallic liquid acting as an electrode.